Torn-up galaxy hints at Milky Way's fate

Astronomers watch spiral galaxy being ripped apart

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An artist's rendering shows how gas in C153 is compressed along its leading edge, like snow before a plow, igniting a storm of starbirth. The pressure of hot gas trapped in the cluster strips away the galaxy's own cooler gas, leaving behind skeletal spiral arms of dust and stars.

ATLANTA — The newly witnessed demise of a galaxy has given astronomers a glimpse into the lives and deaths of spiral galaxies in a violent universe, and possibly a view of the ultimate fate of the Milky Way.

Once like the Milky Way, the ill-fated spiral galaxy C153 ripped through the heart of a distant galactic cluster at 4.5 million mph (2,012 kilometers per second), being shredded along the way. As the galaxy careens away from the cosmic collision, gas trails in streams 200,000 light-years long.

"Its entry into the cluster has created the perfect storm," astronomer William Keel of the University of Alabama said of C153. The destruction is happening "all at once, instead of spread out over a billion years."

Other galactic collisions typically involve partial distortion of one or both galaxies as a long, orbiting dance ensues. This was a head-on collision.

Studying spiral galaxiesKeel and a team of researchers studied the C153 smash-up as part of a broader investigation into spiral galaxies. According to past observations, rich galactic clusters in the early universe were flush with spiral galaxies, only to have numbers diminish as time progressed. Consumption by those clusters during an errant collision, astronomers say, may explain the cosmic evolution.

"It’s a very visual thing, this transformation of galaxies," Keel said. "But it has been difficult to see because clusters are such busy environments, with so many things happening at once."

Keel and his colleague, Daniel Wang from the University of Massachusetts, announced their research here Tuesday at a meeting of the American Astronomical Society. Astronomers Frazier Owen of the National Radio Astronomy Observatory and Michael Ledlow at the Gemini Observatory also participated in the study.

Death plunge
Using optical, X-ray and radio telescopes, Keel and his colleagues were able to deconstruct the death plunge of C153 as it was stripped of its gas by the collision, leaving only its skeletal spiral arms in place. The free gas, however, is being put to work making new stars in the core of the galactic cluster, dubbed Abell 2125, which sits about 3 billion light-years from Earth.

Keel's team first noticed the doom of C153 while studying Abell 2125 in the 1990s. Researchers were using the Very Large Array radio telescope near Socorro, N.M., when they detected the unusually high population of radio galaxies in Abell 2125. The spiral C153, it turned out, was among the post powerful of those galaxies.

NASA / NRAO / Gemini / UMASS

A spiral galaxy is ripped apart as it races at 4.5 million miles per hour through the heart of a distant cluster of galaxies. The observations provide evidence in the form of gas being stripped from the doomed galaxy, called C153.

"It’s the brightest compact galaxy in the entire cluster," said Wang, who used NASA's orbiting Chandra X-ray Observatory to study the stream of gas being stripped from C153. "In 100 million years or so, though, it will lose all its gas in the collision."

Hubble Space Telescope observations of C153 showed a clumpy object with a large number of young stars and chaotic dust formations. Besides disruptions in the galaxy’s disk, Hubble images showed signs of recent star formation in the wake of the galaxy, as well as along the leading edge of C153, where some gas is compressed into stellar birth.

But the majority of available gas is being blown back like the air around a speeding car, Wang said.

Eventually, the galaxy will lose the last trappings of its spiral arms, with only a central bulge and disk to hint at its previous spiral-armed existence. Such galaxies are common in dense galactic clusters seen today. Keel and his team hope to make more observations of C153’s tail structure later this year to study the dynamics of gas and stars in the trailing tail.

Our own fate?
The death of C153 provided astronomers one possible future for our Milky Way galaxy as it moves through its own galactic neighborhood, the Virgo Cluster. While the galaxy is still in the outskirts of the Virgo Cluster, it could plummet into the cluster in 50 billion to 80 billion years time.

"The Milky Way has been very lucky," Wang said. "It still is in the [cosmic] suburbs or countryside."

Other studies indicate the Milky Way is headed for an eventual collision with the Andromeda Galaxy, another large spiral. Computer models indicate that crash will result in a merger of the two galaxies.